A new generation of optoelectronic devices such as organic photovoltaics (OPVs), organic field-effect transistors, organic photodetectors, and organic light-emitting transistors (OLETs) are fabricated using organic semiconductors as their active components. To be commercially relevant, these organic semiconductor-based devices should be processable in a cost-effective manner while meeting certain threshold device performance criteria.
Bulk heterojunction (BHJ) solar cells commonly are considered the most promising OPV structures because they can be fabricated using roll-to-roll and large-scale production. BHJ solar cells include a photoactive layer disposed between an anode and a cathode, where the photoactive layer is composed of a blend film including a “donor” material and an “acceptor” material. State-of-the-art BHJ solar cells use fullerene-based compounds as the acceptor material. Typical fullerenes include C60 or C70 “bucky ball” compounds functionalized with solubilizing side chains, such as C60-[6,6]-phenyl-C61-butyric acid methyl ester (C60-PCBM) or C70-PCBM. The most common donor material used in BHJ solar cells is poly(3-hexylthiophene) (P3HT). However, it is well known that P3HT has poor air stability. Also, it has proven challenging to attain an overall power conversion efficiency (PCE) over about 5%.
Meanwhile, despite extensive research on organic photodetectors in the past decade, there have been few reports of organic donor materials that provide efficient absorption in near-infrared (>700 nm) photodetectors.